Testing is a key enabling technology in the art of integrated circuit manufacturing. Typically, testing is performed at the wafer-level and at the package level. When a device is tested at the wafer level, coupling between the device under test (“DUT”) and the automated test system is made possible using a probe card. Referring to FIG. 1, a simplified, automated test system is shown. Automated test equipment (“ATE”) 10 conventionally includes a high speed and high precision testing circuit. The ATE 10 is coupled to a wafer prober station 14. The wafer prober 14 contains a test head or probe head 18. Wafers are loaded into the test head where they are placed on a wafer stage for testing.
The automated test system is typically a very expensive tool. It is therefore designed as a general-purpose tool to test a number of different integrated circuit designs. Flexibility of use is derived by storing a number of testing programs in ATE 10 that may be selected by the user interface 22 prior to each test. In addition, it is well-known that integrated circuit devices employ a variety of input/output (“I/O”), power and ground pins or terminals. Therefore, the test system must be able to account for these differences. Conventionally, this flexibility is derived by using probe cards.
A probe card is an interface card between the probe head 18 and the DUT. The probe card translates the fixed pin-out capabilities, such as hard wired input channels or output channels of the ATE into a flexible arrangement of pins custom interfaced to a specific IC design. Thus, ATE system 10 can be used to test a number of different designs using a common, and often quite expensive, probe head 18.
Referring to FIG. 2, an exemplary probe card 30 and integrated circuit 38 combination is shown in top view. The integrated circuit die 38 comprises internal circuitry connected to pads 42 that ring the periphery of the device. Pads 42 may comprise bonding pads. A bonding pad is typically a metal pad to which a metal wire is bonded or welded in order to create an interconnection between the device and circuitry of an encapsulating package. Probe card 30 comprises a corresponding set of probe pins 34 that are aligned to physically touch each of the probe pads 42 of the DUT. Probe card 30 couples these probe pins 34 to interconnecting metal lines in the probe card structure that can connect to the probe head of the ATE system when the card 30 is installed in the probe head.
Referring to FIG. 3, a cross sectional view of the probe card 30 in combination with integrated circuit device 38 is shown. Conventionally, many circuit die 38 are formed on a single wafer. In this example, a single die 38 is contacted by probe card 30 for testing. In practice, multiple dies can be probed at one time. The wafer is placed onto a wafer stage 50 and may be further held in place using vacuum or mechanical means. Probe card 30 is fixably attached to the probe head to provide electrical coupling to the ATE and to allow alignment and vertical movement. In a typical arrangement, the probe card 30 is aligned to the wafer under test at a first die location on the wafer. After successful alignment, the probe card 30 may then be indexed across the wafer to test each die 38. Probe card 30 is engaged for testing by vertically moving the card down until the probe pins 34 contact the probe pads 42.
Referring to FIG. 4, an additional exemplary integrated circuit device 60 is shown. Pads 64 are again included around the periphery of the device 60. In this case, however, the integrated circuit device 60 is a flip chip device. In a flip chip device, raised bumps 68 are formed on the surface of the chip. Instead of wire bonding the die to a package, circuit die 60 is flipped over and attached directly to a system-level circuit, such as a circuit board or a ceramic (or Organic) substrate. To facilitate direct connection, the raised bumps commonly comprise a top layer of solder that can be easily melted to create a permanent connection to the circuit board. In the exemplary case, the solder bumps are connected to the wire bonding pads using a redistribution layer 72, such as metal lines.
Referring now to FIG. 5, another probe card is shown in cross sectional view. The probe card is a vertical probe card comprising a probe head 80, probes 84 and bottom guide plate 88. Vertical probe cards are commonly used for flip chip devices. Typically, vertical probe cards require 3 to 4 months to fabricate. The vertical probe technology uses vertical probes that match the pattern of the pads on the IC being tested. This technology allows for the probing of pads in the center of an IC (area array) and is used generally for high-density applications. More importantly, each integrated circuit design requires a customized card to fit the dimensions and pin out of the device. Due to the long fabrication time and the fragility of the probe cards, the integrated circuit manufacturer must purchase several vertical probe cards for each device in case the probe card breaks. Moreover, the probe cards are not universally applicable and a new probe card must be designed for testing new dies.